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Serotonin is an important neurotransmitter that promotes a healthy sleep cycle, decreases anxiety and depression and promotes well-being and happiness. Although soy does not contain serotonin, it contains three compounds that influence serotonin production: tryptophan, isoflavones and complex carbohydrates. In addition to the potential benefits of increased serotonin levels, eating more soy is a good way to introduce complete plant proteins to your diet.

Amino Acids

Your body requires 20 different amino acids for optimal, regular functioning. Although it is able to synthesize 11 of these, your body cannot produce the remaining nine "essential" amino acids. These amino acids must be obtained from dietary sources. Protein foods that provide all of the essential amino acids are called "complete proteins," and soy is one of the few non-animal complete proteins. This property is one of the explanations for soy's potential mood-enhancing effects.

Tryptophan

A 1-cup serving of tofu contains 89 percent of your recommended daily intake of tryptophan. This essential amino acid serves two important roles in your body. It is essential to your body's ability to produce niacin. Although you can also obtain this important B-vitamin from dietary sources, your body can synthesize it from tryptophan if you have an adequate intake of iron, riboflavin and vitamin B-6. A second important feature is tryptophan's role in your body's production of serotonin. Both niacin and serotonin are related to healthy cognitive functioning, including decreased levels of depression and anxiety.

Isoflavones

Soy is the best dietary source of isoflavones, which act as phytoestrogens in your body. Also known as dietary estrogens, these compounds help to regulate sex hormones in your body and reduce your risk of breast and other cancers. In addition, isoflavones may be able to increase your body's serotonin production. Soy phytoestrogen intake increases levels of both the serotonin reuptake transporter protein and an enzyme essential to breaking down tryptophan. Together, these compounds influence your body to produce greater amounts of serotonin.

Complex Carbohydrates

Complex carbohydrates are typically lower in sugar and take longer for your body to break down than simple carbohydrates. Soybeans and soy products are sources of complex carbohydrates. For example, a 1-cup serving of unsweetened soy milk contains 4.2 grams of carbs -- or 3.2 percent of your recommended dietary allowance -- but only 1 gram of sugar. According to MayoClinic.com's Dr. Daniel Hall-Flavin, complex carbohydrates have the additional benefit of increasing the amount of serotonin in your brain. This provides an additional route by which soy increases serotonin levels.

About the Author

Matthew Lee has been writing professionally since 2007. Past and current research projects have explored the effect of a diagnosis of breast cancer on lifestyle and mental health and adherence to lifestyle-based (i.e. nutrition and exercise) and drug therapy treatment programs. He holds a Master of Arts in psychology from Carleton University and is working toward his doctorate in health psychology.